| Power system may be in the state of emergency when the second kind of faultdisturbance occurs during normal operation or when the first kind of fault occurs duringthe emergency state. Emergency control measures should be taken immediately to preventpower system operation state deteriorating under the state of emergency. Experienceshows that the lack of due attention to power system emergency control is the main reasonwhy the power system operation state evolves from the state of emergency to the state ofcollapse. That is why it is of great significance to study the stability control methods ofpower grid to maintain the security and reliability of it. In weak power grid, there arefewer units, the capacity of single unit is smaller and the grid is weaker compared withlarge power grid, which makes stability problems more likely to arise. Among all thestability problems, the frequency issue is particularly acute. With the continuous increaseproportion of wind power and other renewable energy, the power system is now facing theincreasing pressure of maintaining frequency stability and research on frequencyemergency control has to be carried out immediately. Therefore, weak power gridfrequency emergency control method with large scale wind power integration is studied inthis paper.In this paper, frequency characteristics influencing factors of weak power grid arefirst analyzed based on the frequency characteristic general rules of large-scale power gridby contrast. Simulation research is carried out based on the three-machine nine nodesmodel and the real weak power grid. Second, in view of the situation that large scale windpower penetrates in weak power grid, new frequency characteristics are analyzed both intheory and by simulation considering that different types of wind turbines connect intoweak power grid (such as direct drive permanent magnet wind turbine, doubly fedinduction wind turbine and fixed speed wind turbine), wind power penetration changesand that wind power fluctuates. Third, on the problem that load shedding andunder-frequency load shedding measures can hardly coordinate with each other, thecoordination scheme is put up. Fourth, the adaptability of the original under-frequencyload shedding scheme is analyzed both in theory and by simulation when wind powerpenetrates in weak power grid, based on which new under-frequency load sheddingscheme is proposed when wind power penetrates. The adaptability of the new method isverified via the simulation system. At last, for weak power grid with wind power penetration, the coordination scheme of load shedding and under-frequency load sheddingmeasures is proposed under various work conditions. Frequency exceeding the limits as aresult of excessive load shedding can be avoided effectively with the proposedcoordination scheme. The coordination flow chart of frequency emergency controlmeasures of weak power grid with wind power penetration is established. |
